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Chapter 6 / Missile Guidance
_ _
∂ F
∂ P
XB
T
ZG
d,
m
: =
⎛
6
6.
7881 x 10 ⎞ ∂ P
− ⎜
⎟
⎜
⋅
0.
833 XB
PS
F ⎟
⎝ ⋅ T ⎠ ∂ P
6-6
S
ZG
d,
m
Equation 6.3-4
Short-boosting missiles remain in the Troposphere in which case the
variation in static pressure is given by Equation 19.1-4.
6.4 Missile Drag
The boost and coast phase drag depends on Mach number (Mm) and air
density (ρA) defined in §19.3, also missile speed and body incidence ( MV
ξ B )
defined in §16.6,
D
XB
D
−1 2 2
⋅ π ⋅ ρA
⋅ dm
⋅ P&
d,
m
F : = − 8
⋅ C
ij
i
MV
MV
( M ) ⋅ N ( 24 ⋅ ξ
)
C : = CD ⋅ M
ξ
m
j
B
D
MAX
Equation 6.4-1
B
Equation 6.4-2
The drag coefficient (CD) is determined using the B-splines coefficients
(CDij) listed in Table 6-1 for Mach numbers [1,4], and body incidence
[0,24°]. The boost phase variation in (CD) for Mach numbers and incidence
up to 3.5 and 15° respectively is shown in Figure 15-1.
BOOST PHASE COEFFICIENT
1.4
1.2
1
0.8
0.6
0.4
0.2
1 1.5 2 2.5 3 3.5
MISSILE MACH NUMBER
SIGMA = 0 deg
SIGMA = 5 deg
SIGMA = 10 deg
SIGMA = 15 deg
Figure 6-2 : Boost Phase Drag Coefficient
The equivalent coast phase drag (not shown) is larger as the effective
missile surface area increases without the motor plume. To accommodate
variations in maximum incidence (σMAX), defaulting to 40°, the output from
the B-splines are scaled by 40/24. The drag function state dependencies are,